The application of summoning emergency assistance by using a phone to call 9-1-1 has been ingrained in our society for 40+ years. A successful emergency response is dependent upon the responders receiving accurate location information to effect timely action. Traditional wireline telephony is able to utilize the location of the physical wires as a source of information for caller location, whereas wireless technologies require more exotic mechanisms to locate a 9-1-1 caller.
The industry accepted practice for locating a wireless 9-1-1 caller actually employs a multi-step process. The timing of the various steps is important such that the human caller does not get impatient and abandon the call prior to talking to the Public Safety Answer Point (PSAP). The mechanism(s) used to determine the location of a wireless device takes time, and this amount of time is typically more than expected for a normal wireline phone call to get answered. As a result, some people, in frustration, may have a tendency to hang-up, assuming something is wrong when the call does not go through in a few seconds. This frustration may be exaggerated during a time of stress in an emergency situation. In addition, since the number 9-1-1 resembles an anycast destination (i.e., it should be routed to the nearest destination node in a group of potential receivers), a rough location of the caller must, in the first instance, be determined in order to decide which PSAP to route the call to. Hence, the industry uses a multi-step procedure, starting with cell tower location associated with the call to determine the correct PSAP for call routing. A more precise caller location determination occurs during the call, after the initial call setup.